Crystal structures of 4-[(4-methylbenzyl)oxy]benzohydrazide and its N′-[(thiophen-2-yl)methylidene]- derivative

The crystal and molecular structures of a benzoylhydrazine bearing an ether group and of its N′-[(thiophen-2-yl)methylidene derivative are reported and compared.

In the context given above, we report on syntheses and crystal-structure determinations of two related compounds, viz. a benzoylhydrazine bearing an ether group (I), C 15 H 16 N 2 O 2 , and the corresponding N 0 -[(thiophen-2-ylmethylidene) derivative (II), C 20 H 18 N 2 O 2 S.

Structural commentary
The molecular structure of hydrazine compound (I) is shown in Fig. 1. The N1-N2 and the O2 C15 bond lengths of 1.4200 (15) and 1.2388 (15) Å are indicative of a single and double bond, respectively. All other bond lengths are as expected when compared with molecules of similar hydrazine and hydrazone compounds (Wang, Zhou et al., 2014;Wang, He et al., 2014;Fun et al., 2012;Zong & Wu, 2013). The conformation of the molecule shows the central phenyl ring (C9-C14) of the benzoyl mean plane forming a dihedral angle of 66.39 (3) with the 4-methylbenzyl group (C1-C8), and it is also rotated slightly [by 28.49 (6) ] with respect to the mean plane through the C O-NH-NH 2 moiety.
The molecular structure of hydrazone derivative (II) is shown in Fig. 2. The thienyl (C17-C20, S1) ring and the central phenyl ring (C9-C14) are linked by the acyl-hydrazone (-CH N-N-CO-) group. An E-configuration is observed with respect to the double bond of the hydrazone bridge N2 C16. Compared to (I), the N1-N2 bond length of 1.397 (4) Å appears slightly shorter, most probably caused by a different intermolecular hydrogen-bonding interaction. On the other hand, the O2 C15 bond of 1.236 (4) Å , is nearly identical with that of (I) and is typical for a ketonic linkage in the solid state, while an equilibrium between the keto and enol form is present in solution. The molecule has the thienylmethylene and the benzohydrazone fragments almost coplanar, with maximum deviations of À0.234 (3) and +0.392 (2) Å exhibited by atoms C10 and O2, respectively. The terminal 4-methylbenzyl group is rotated by 55.87 (9) with respect to the central phenyl ring, similar to the dihedral angle observed in (I).
A superimposition of the two molecules (shown in Fig. 3) highlights their conformational differences: while the 4-[(4methylbenzyl)oxy] benzoyl groups almost overlap, it is worthy to note the different orientation of the carbohydrazide C O-NH-N moieties, likely induced by crystal packing effects to favor hydrogen-bonding interactions.

Supramolecular features
Classical hydrogen-bonding interactions represent the main contributions to the packing of the molecules in the crystals of (I) and (II); numerical data are compiled in Tables 1 and 2, respectively.
In (II), the number of conventional hydrogen bonds is considerably reduced. The corresponding N1-H1NÁ Á ÁO2 i [symmetry code: (i) Àx + 1 2 , y À 1 2 , z] interactions create an undulating ribbon parallel to [010], as displayed in Fig. 6 Molecular structure of (I), with displacement ellipsoids drawn at the 50% probability level.

Figure 2
Molecular structure of (II), with displacement ellipsoids drawn at the 50% probability level.

Figure 3
Overlay plot of molecules (I) and (II) to show the conformational difference.

Figure 5
The layered arrangement in the crystal packing of (I) caused by additional N-HÁ Á ÁO interactions.

Figure 6
The chain structure in the crystal packing of (II) with indication of N-HÁ Á ÁO hydrogen bonds (orange dashed lines). Table 1 Hydrogen-bond geometry (Å , ) for (I).

D-HÁ
2 h. A white precipitate was obtained, filtered off, and washed several times with hot ethanol, and finally dried over silica gel in a desiccator. A small amount of the compound was dissolved in 25 ml of absolute ethanol and allowed for slow evaporation. Suitable crystals for single-crystal X-ray diffraction were collected after 30 d of keeping the sample solution undisturbed. Yield: 0.86 g, 50%; melting point: 505-506 K. We failed to locate the 1 H NMR signals of Ar-H 3,4 and of thiophene ring hydrogen atoms, likely due to the poor solubility of the compound in organic solvents.

4-[(4-Methylbenzyl)oxy]benzohydrazide (I)
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

4-[(4-Methylbenzyl)oxy]-N′-[(thiophen-2-yl)methylidene]benzohydrazide (II)
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.28 e Å −3 Δρ min = −0.46 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.